Currently, a mainstream of computer architecture lies in Neumann type computer. The basic operation of the Neumann type architecture is to sequentially execute instruction strings. Enhancement in the performance of a computer has mainly depended upon the enhancement of a clock frequency. However, recently, in place of the clock frequency that reaches the peak, a method of realizing the enhancement of performance with parallel processing by multicoring is a mainstream.
In the parallel processing by multicoring, performance is enhanced by finding a location where parallel execution is possible in serial instruction strings (extracting parallelism) and executing parallel processing. However, it is not easy to extract parallelism from a program in which serial algorithm is written in the form of instruction strings.
In view of such a situation, to enhance the performance of a computer hereafter, essential conversion to parallel information processing without being based upon the execution of serial instruction strings as heretofore is required. A method of describing a subject suitable for realizing essential parallel information processing is then required in place of the past method of describing a subject by serial instruction strings.
Various physical phenomena and various social phenomena can be represented by an interaction model. The interaction model means a model defined by plural entities or plural nodes that configure the model, interaction between the entities and further, bias for every entity if necessary. In physics and social science, although various models are proposed, any can be interpreted as one configuration of the interaction model. Besides, for a characteristic of the interaction model, it can be given that an effect among entities is limited to interaction between two entities. For example, the dynamics of planets in cosmic space can also be interpreted as one type of the interaction model because interaction by universal gravitation exists between entities called planets. However, an effect among the planets is not limited to that between two planets. Three or more planets have an effect upon one another, and show complex behavior (a problem respectively called a three-body problem and a many-body problem). For one example of the interaction model, Ising model can be given. The Ising model means a model of statistical mechanics for explaining the behavior of a magnetic body and is used for the research of the magnetic body. The Ising model is defined as interaction between sites (spins that take two values of +1 and −1). It is known that search by topology for a ground state of the Ising model to be a nonplanar graph is an NP-hard problem. The Ising model may be able to realize information processing utilizing essential parallelism because the Ising model represents the problem by interaction coefficients that spread in space.
As the search of the ground state of the Ising model is the NP-hard problem as described above, it is difficult in terms of computation time to acquire the solution by the Neumann type computer. Algorithm for accelerating using heuristics is also proposed while a method is proposed in which the ground state of the Ising model is computed at high speed by not the Neumann type computer but an analog computer that computes more directly utilizing physical phenomena.
For such a device, a device disclosed in WO 2012/118064 for example can be given. In such a device, a degree of parallelism corresponding to a subject to be solved is required. In the case of the Ising model, elements that realize spin and interaction corresponding to the number of spins in the Ising model which should search the ground state are required. In the device disclosed in the WO 2012/118064 for example, spin and a laser are made to correspond and lasers of the number proportional to the number of spins are required. That is, the height of scalability that can realize multiple elements is required.
Besides, in the world of biology, a neural network that models a brain is one example of the interaction model. The neural network is based upon an artificial neuron that models a neuron and artificial neurons have interaction called connection by a synapse. Moreover, bias may also be applied every neuron. In the world of social science, considering communication between persons for example will make it easy to understand that interaction made by language and communication exists between entities called a person. In addition, it can also be imagined that bias exists individually in each person. Therefore, research to clarify a characteristic of human communication in the Ising model common in the terms of the interaction model and others is also done (for example, refer to JP-A No. 2012-217518).
Further, as disclosed in Japanese Unexamined Patent Application Publication No. 2011-524026, an attempt to search the ground state of the Ising model utilizing quantum mechanical effect in a superconducting device is also made. The quantum mechanical effect means to utilize a so-called superposed state, to utilize the superposition of spin states, and to try to enhance the performance of convergence.
However, from a viewpoint of scalability, an approach different from the abovementioned device is demanded. That is, to realize the more number of spins, a large number of lasers are required to be arranged and a superconducting device that requires advanced cooling technique has a limit. A method of acquiring great scalability more simply is required. It is a semiconductor device (a semiconductor integrated circuit) that is the best in scalability in the current packaging technique. In the semiconductor integrated circuit, circuits are formed over a semiconductor substrate made of silicon and others by a method similar to printing technique called photolithography. Besides, the size of elements and wiring which can be respectively formed on/over the semiconductor substrate is reduced year by year (it is called the microfabrication of a semiconductor device), and a circuit scale which can be packaged in the same area is growing larger year by year.
The high scalability of the semiconductor integrated circuit has supported the enhancement of the performance of the Neumann type computer. However, in the abovementioned new type of computer, a realizable embodiment as a semiconductor device having high scalability will be also demanded.